[SI-LIST] Re: Do you ever measure any of the things you model?

From: "Tony Dunbar" <tony.dunbar@xxxxxxxxxxxxxxxxxx>

To: <si-list@xxxxxxxxxxxxx>

Date: Mon, 31 Mar 2008 19:40:44 -0500

Hi,
In my view, the situation we are in regarding model quality is largely the
fault of the end-user community. Over the years, many people I've worked
with have heard me tell them never to under-estimate the power they have
with silicon vendors based on the company they work for when it comes to
demanding to have verified models. I'm talking, in many cases, multi-billion
dollar companies. I've advocated that they get their VP of Engineering or
other suitably high-level officer to communicate their requirements (or
demands) to his equivalent at the silicon vendor company. As Scott has
pointed out, unless it's tied to revenue (or lack thereof), no notice will
be taken and no progress will be made. That's capitalism. Another
unfortunate reality of capitalism is that the demander must have the clout.
That's where the multi-billion dollar companies come in. It's up to them to
drive this so that everyone benefits.
Funny side note is that I once said to someone, 'After all, if this was a
VHDL or Verilog model we were talking about, you wouldn't tolerate garbage,
would you?' I was told I might be horribly surprised to learn things aren't
so rosy in that world either.
Thanks!
Tony
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Joel Brown
Sent: Monday, March 31, 2008 6:18 PM
To: 'Alfred P. Neves'; 'Tom Dagostino'; 'Schumacher, Richard (HSTD Signal
Integrity)'; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Do you ever measure any of the things you model?
It seems that the voluntary system of IBIS compliance is broken.
Actually compliance is not the right word because we don't hold anybody
accountable for distributing bad models.
Not only that, some companies don't offer models on parts they should and
sometimes it requires signing NDAs and waiting three months to get a model
(that actually happened to me).
There is no counterpart to IBIS in the PDN world and there should be because
we can't guess at any accuracy what the on chip PDN and power spectrum are
which really makes it difficult to "design" the board PDN.
When we all have to comply with and pass regular ISO audits in our work
environments, it seems that the equally important discipline of SI and PI
have no such standards to live up to. While a completely voluntary system is
desirable, it clearly is not working well. When will the industry wake up
and do something about this?
End of rant.
Joel
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Alfred P. Neves
Sent: Monday, March 31, 2008 3:47 PM
To: 'Tom Dagostino'; 'Schumacher, Richard (HSTD Signal Integrity)';
si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Do you ever measure any of the things you model?
Adding to what Tom already said... My personal experience working at
numerous semiconductor companies marketing high speed products (both =
digital and analog oriented, including PHY's, SERDES, etc.,) is that they =
typically select a design engineer that generates the IV and VT curves,
along with dynamic characteristics with only simulations, no measurements.
=20
Unfortunately, since design engineering time is expensive and the good =
ones are VERY busy designing new products, to my experience (not a rule, and
= not meant to insult any engineers who pride themselves in this effort) it
= was not always the most experienced or talented engineer that was
designated = for this activity. =20
This all of course assumes the design represents the process variations, =
the package model was included in the full simulation suite and the =
simulation was set up and performed correctly.
Anyhow, I recall a significant number of customers complaining that the
models either would not work at all (a test parser was not run) or they
poorly matched measurements. =20
Maybe it is the geek in me, but it sends tingles up my spine when my
simulations match almost perfectly to measure-based results.
Alfred P. Neves=A0=A0=A0=A0=A0 <*)))))><{=20
Hillsboro Office:=20
735 SE 16th Ave.=20
Hillsboro, OR, 97123=20
(503)=A0718 7172=A0 Business=20
(503)=A0679 2429=A0=A0 Mobile=A0
=A0=20
Main Corporate office:=20
Teraspeed Consulting Group LLC=20
121 North River Drive=20
Narragansett, RI 02882=20
(401) 284-1827 Business=20
(401) 284-1840 Fax=20
http://www.teraspeed.com=20
=A0=20
Teraspeed is the registered service mark=20 of Teraspeed Consulting Group
LLC=20
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Tom Dagostino
Sent: Monday, March 31, 2008 2:54 PM
To: 'Schumacher, Richard (HSTD Signal Integrity)'; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Do you ever measure any of the things you model?
Richard
We measured one Quellan device for the model and used a different device =
for the system test. When we measure a device we vary it's temperature and
supply voltage over the datasheet's operating limits. We usually do not =
get process corner sample but if we did we would have used the strong fast
corner at the cold high voltage operating point and the slow weak corner =
at the hot low voltage point for a CMOS device. This would have given a
complete process/temperature/voltage model. =20
But what we have seen from much experience is the IV and VT curves of = the
random devices we get are very consistent from part to part of the same
manufacturing process. When I say part to part we are including both the
different die of the same part number and different part numbers from = the
same process. We see stronger effects from temperature and voltage than = we
see from process variation.
Regards
Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
503-430-1285 FAX
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827=20
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Schumacher, Richard (HSTD Signal Integrity)
Sent: Monday, March 31, 2008 2:19 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Do you ever measure any of the things you model?
Drifting the topic a little:
"[...] developed a measure-based IBIS model of the Quallan equalizer [...]
We were able to achieve excellent correspondence between system = simulation
=3D and measurements (a few psec correspondence for a 10Meter length signal
= pat=3D h, see page 36) made with our DSO. The correspondence was very
much = =3D3D du=3D e to the quality of the model in that it was generated
with very = carefully =3D acquired measure-base data using a high signal
integrity fixture, fast = TDR =3D head, etc.
I checked the IBIS model separately and it looked exactly like measured =
dat=3D a in terms of not just rise/fall time in an eye diagram but also the
= pedest=3D al and features of the eye were captured extremely well. I have
found = IBIS=3D model accuracy to be critical, and unfortunately most of
the vendor = based =3D models are a bit disappointing in their
representation.
Check it out:
http://www.home.agilent.com/upload/cmc_upload/All/SI3_Teraspeed_Equalizat=
io=3D
n06.pdf "
To be precise, this uses an IBIS model of a specific instance of the =
Qualla=3D n RX, true? In other words parameters such as silicon
characteristics, = ope=3D rating temperature, supply voltages, channel
impedances etc. were = identical=3D in both the system and in the
measurement-based model of that system. = How=3D good is the agreement
when that same IBIS model is used to simulate = anothe=3D r instance of the
same device type, or when that same device instance is = op=3D erated at
different but within-spec values for temperature or voltage?
Could an IBIS model of the TX be used?
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